I knew the clutch master was new/aftermarket (still need to repaint where it leaked on the inside of the firewall) and I replaced the slave - but, I didn't realize the brake master was - the booster probably is too.
I wasn't worried about the cant, just curious - thanks!
The booster looks stock for a '78.
There is normally a small, black, flat clip that holds the check valve in position. I just happened to see it missing from your photo. You can barely see it attached to the white post of the check valve in the photo of post #2. (I'm not saying that you need to mess with the check valve. I just noticed the clip missing. The check valves tend to be very brittle and they are difficult to find nowadays.)